Electrical regulator apparatus including a zero temperature coefficient voltage reference circuit

ABSTRACT

An integrated circuit regulator including a temperature stable constant voltage reference wherein the negative temperature coefficient of the base-to-emitter voltage a first transistor in conjunction with the positive temperature coefficient of the base-to-emitter voltage differential between two additional transistors operating at different current densities is used to achieve a zero temperature coefficient reference potential. The constant voltage reference is combined with a voltage follower and provides a source of constant current which is passed through an external variable resistance to develop a selectable and predictable adjustment voltage for driving the voltage follower so as to cause an unregulated input voltage applied thereto to be regulated at an output terminal.

United States Patent [72] Inventors Robert C. Dobkin Menlo Park; RobertJ. Widlar, Mountain View, both of Calif.

[21] Appl. No. 21,968

[22] Filed Mar. 23, 1970 [45] Patented Nov. 2, 1971 [73] AssigneeNational Semiconductor Corporation Santa Clara, Calif.

[54] ELECTRICAL REGULATOR APPARATUS INCLUDING A ZERO TEMPERATURECOEFFICIENT VOLTAGE REFERENCE CIRCUIT 12 Claims, 4 Drawing Figs.

[52] US. Cl 323/4,

[51] Int. Cl G05f 1/58 [50] Field of Search 307/296,

[56] References Cited 'UNITED STATES PATENTS 3,205,458 9/1965 Geery330/23 X IN c r Primary Examiner-A. D. Pellinen Assistant Examiner-A. D.Pellinen Attorneys-Harvey G. Lowhurst and A. S. Claude Hamrick ABSTRACT:An integrated circuit regulator including a temperature stable constantvoltage reference wherein the negative temperature coefficient of thebase-to-emitter voltage a first transistor in conjunction with thepositive temperature coefficient of the base-toemitter voltagedifferential between two additional transistors operating at differentcurrent densities is used to achieve a zero temperature coefficientreference potential. The constant voltage reference is combined with avoltage follower and provides a source of constant current which ispassed through an external variable resistance to develop a selectableand predictable adjustment voltage for driving the voltage follower soas to cause an unregulated input voltage applied thereto to be regulatedat an output terminal.

PATENTEDNUV 2 I97! 3,617, 8 59 SHEET 10F 2 /0 up L m l I l4 T VOLTAGE E.I REFERENCE I 4 I v J 1 34| v l4 20 1 /6 I 26 l I R 32 Q2 283 l I oP. L36 AMPL.

INVENTORS ROBERT C. DOBKIN BY ROBERT J. WlDLA-R PATENTEnunv 2 |97| SHEET2 [IF 2' VOLTAGE REFERENCE INVENTORS ROBERT C. DOBKlN ROBERT J. WIDLAR EATTORNEY ELECTRICAL REGULATOR APPARATUS INCLUDING A ZERO TEMPERATURECOEFFICIENT VOLTAGE REFERENCE CIRCUIT BACKGROUND OF THE INVENTION 1.Field of The Invention The present invention relates generally toelectrical regulator apparatus and, more specifically, to a novelfloating voltage regulator circuit suitable for integrated circuitapplications and capable of providing regulation over substantially anyvoltage range. The regulator can also be modified in accordance with theinvention to provide a current regulator.

2. Discussions of The Prior Art Standard voltage regulators usuallyconsist of an internal voltage reference, an error amplifier and a poweroutput stage. The error amplifier compares the internal reference with afraction of the output voltage and drives the output stage to keep thetwo voltages equal. One of the disadvantages of this type of regulatorconfiguration for integrated circuits is that the minimum input voltageis equal to the internal reference voltage. Since the reference istypically provided by a zener diode, the minimum input voltage islimited by the 7- volt breakdown of integrated zener diodes. Mostregulators thus cannot operate at very low voltages unless they employtwo separate power supplies.

Prior art voltage regulators of the integrated circuit type usually havea reference voltage which is generated by a zener diode voltagereference source. The zener diode, however, is still not well understoodeither mathematically or theoretically and consequently, obtaining astable zener diode is primarily a matter of chance based on cut-and-trymethods of careful selection and measurement. Once a suitable zener isobtained, the only available voltage range for zero temperaturecoefficient is that of 6 or 7 volts and upward.

Integrated circuit floating voltage regulators have been provided in theprior art which utilize an ordinary zener diode as an externalreference. Such circuits, however, require that the input voltage mustbe at least 6 or more greater than the output voltage. This makes for aninefficient regulator in that there is always a wide variation betweenthe required supply voltage and the regulated voltage. For example, ifone requires a l-volt regulator, he will need at least 16 volts input tosupply it. Zener diodes having low temperature coefficients at 6 or 7volts are readily available but there is no available reference that hasa a zero temperature coefficient at voltages much less than 6 volts.

A practical floating regulator should have a reference of less than 6 toeliminate the disadvantages associated with a 6-volt or greaterinput-output voltage differential.

OBJECTS OF THE INVENTION it is therefore a primary object of the presentinvention to provide a novel general purpose electrical regulator havinga regulatable output voltage which is adjustable down to 0 volts.

Another object of the present invention is to provide a novelthree-terminal voltage regulator suitable for integrated circuitapplications and capable of providing voltage regulation at any outputvoltage.

Still another object of the present invention is to provide a novelvoltage regulator circuit suitable for integrated circuits and includinga new type of internal voltage reference circuit having a zerotemperature coefficient.

Still another object of the present invention is to provide a noveladjustable floating voltage regulator that can be made in monolithicintegrated circuit form and encapsulated in a standard three-terminaltransistor package, thus avoiding the problems of multilead lC powerpackages.

SUMMARY OF THE PRESENT INVENTION In accordance with the presentinvention, a novel electrical regulator circuit is provided which can beused to regulate either voltage or current. The regulator includes azero temperature coefficient transistorized reference circuit andoperational amplifier circuit which cooperate in such a manner as toprovide a general purpose floating regulator circuit having an outputvoltage regulation level that is adjustable down to 0 volts. The circuitis well suited for integrated circuit applications and can be providedin a standard three-terminal transistor power package.

One of the principal advantages of the present invention is that theinternal voltage reference is provided by a temperature stabletransistorized circuit which forms an integral part of the regulator.The reference circuit uses certain basic properties of transistors in aparticular combination to provide a stable low voltage reference for thecircuit.

Another advantage of the present invention is that the entire circuitcan be monolithically fabricated and encapsulated in a standardthree-terminal power transistor package such that the unregulated inputvoltage can be applied to one of the terminals, a variable adjustmentresistance can be connected to another of of he three terminals for usein setting the regulated voltage level, and the regulated voltage can beobtained at the third terminal.

Still another advantage of the present invention is that no zenerdiodes, reverse punch-through transistors, varistors or batteries arerequired to provide the internal reference voltage.

Still another advantage of the present invention is that the internalreference has lower noise, better long term stability and can be betterexplained theoretically than the reference in other prior artregulators.

These and other advantages of the present invention will be apparent tothose skilled in the art after having read the following detaileddisclosure of preferred embodiments which are illustrated in he severalfigures of the drawing.

IN THE DRAWING FIG. 1 is a block diagram showing a three-terminalfloating voltage regulator device in accordance with the presentinvention.

FIG. 2 is a diagram illustrating in detail the voltage reference circuitof the present invention.

FIG. 3 is a schematic circuit showing a preferred embodiment of thepresent invention.

FIG. 4 is a diagram illustrating a current regulator circuit inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to FIG. 1of the drawing, a simplified block diagram of the present invention isshown to illustrate that the invention provides a three-terminalfloating voltage regulator which can be packaged in the standardthree-terminal transistor power package. The circuit 10 includes aninput terminal 1, an output terminal 2 and an adjustment terminal 3which correspond to the three terminals of the standard power transistorpackage. Connected between the input terminal 1 and the output terminal2 is an operational amplifier 12 which is adapted to operate as avoltage follower for regulating an input voltage V,,,, applied atterminal 1 to provide a regulated output voltage V at output terminal 2.The op-amp 12 causes the voltage V at terminal 2 to be the same as thevoltage appearing at terminal 3 in accordance with the normal operatingcharacteristics of a voltage follower circuit, i.e., that the outputvoltage is identical to the input voltage.

The potential appearing at terminal 3 is generated by causing a current1 to flow through an external variable resistance 15 which is connectedbetween terminal 3 and ground. Since the output voltage of a voltagefollower must be identical to the input voltage, the potential V must beidentical to the voltage drop across resistor 15. However, in order torender the voltage drop across resistor 15 predictable for a givenresistive setting, a constant current must be generated and caused toflow therethrough. Accordingly, a voltage reference circuit 14 having azero temperature coefficient is provided which is capable of generatinga constant voltage V across its output terminals 16 and 18 as indicated.The terminal 18 is then coupled to the negative input and the output ofthe opamp 12 and the more positive output terminal 16 is coupled througha resistance R to the positive input of op-amp 12.

One of the characteristics of op-amp 12 is that the potential across thepositive and negative inputs must also be equal to volts. Therefore,since the positive input of op-amp 12 draws negligible current, it willbe seen that 1 reF and since the voltage V is a constant and theresistance of resistor R is constant, the current I flowing throughresistor R must also be constant, The positive input to the op-amp 12draws negligible current, so substantially all of the current I mustnecessarily flow out of the terminal 3 and through the adjustmentresistor 15.

The adjustment voltage V at the positive input of the opamp l2, i.e.,terminal 3, is

ndf rd 15/ where R is the resistance of resistor R, and R, is theresistance of the adjustment resistor 15.

Since the input voltage to op-amp 12 is equal to the output voltagethereof,

ouF reI IS R Turning now to Figure 2 of the drawing, the invention isagain illustrated showing a preferred embodiment of the voltagereference circuit in detail. The voltage reference circuit 14 includesthree matched transistors Q,, Q, and Q;,. In an integrated circuitembodiment, transistors Q,, Q, and Q, are matched by virtue of theirhaving been made at the same time in a single integrated circuit. Thecollectors of transistors Q, and Q, are connected to the circuit point20 through resistors 22 and 24 respectively, while the collector oftransistor 0,, is

5 junction oftransistor Q Thus, by adding equation 4 (with the directlyconnected thereto. The emitters of transistors Q, and

Q,, are directly connected to a circuit point 28, while the emitter of Ois connected thereto through a resistance 30. The base and collector oftransistor Q, are shorted together by lead 32. Circuit point 20 iscoupled to input terminal 1 through a current source 34 and is alsocoupled to output terminal 3 through the resistor R. Terminal 28 isconnected to the negative input terminal 36 of op-amp l2 and the outputof the op-amp while terminal 3 is connected to the positive terminal 38ofop-amp 12.

Voltage reference circuit 14 uses the negative temperature coefficientof the base-to-emitter voltage V of transistor O in conjunction with thepositive temperature coefficient of the base-to-emitter differential AVof transistors Q, and Q which are operated at different currentdensities, to achieve a zero temperature coefficient reference voltage Vacross points 20 and 28. The base-to-emitter voltage V for transistor0,, is given by V, is the extrapolated energy band-gap voltage of thesemiconductor material at absolute zero (about 1.205 volts),

q is the charge of an electron,

n is a constant dependent on the type of transistor (about 1.5 for ICtransistors),

k is Boltzmanns constant,

Tis absolute temperature,

[ is collector current, and

en is the base-to-emitter voltage at T and I The base-to-emitterdifferential AV between the transistors Q, and O, which are operated atdifferent current densities is given by B /q) l 2) where J is currentdensity.

Since transistors Q, and Q are operated at different current densities,the voltage drop across resistor 30 is proportional to thebase-to-emitter differential AV and if the current gains of thetransistors are high, then the voltage drop across resistor 24 is alsoproportional to AV Consequently, the voltlast two terms deleted sincethey are insignificant) to equation 5, V can be expressed as:

r? (kT/q) 111 (11/12) l jifferentiating with respect to temperaturegives For zero temperature coefficient, this expression is equal tozero. Setting the equation equal to zero and substituting into equation(6) gives (8) V ref H Hence, if the sum of V and the voltageproportional to AV equal the energy band gap of the semiconductormaterial, a zero temperature coefficient reference voltage betweenterminals 20 and 28 results. More generally, the reference voltage V canbe expressed as where a, b and c are constants.

As indicated above, current caused to flow through transistor Q will beproportional to the AV between transistors Q, and q: since thebase-to-emitter circuits thereof are connected in parallel. If, forexample, resistors 22 and 30 are of 600 ohms and resistor 24 is of 6,000ohms transistor 0, will run at 1 milliamp and transistor q, will run ata current of microamps. The AV is caused by the fact that transistor Qalso has a certain base-to-emitter voltage, but since the resistor 30 isprovided in its emitter circuit its base-to-emitter voltage V is lessthan that of transistor 0, by an amount determined by the voltage dropacross the resistor 30.

When two transistors such as Q, and are used in this configuration, a AVis generated between them which, at room temperature, is approximately60 millivolts for a 10-1 current difference through the respectivetransistors. Transistor Q, then has 60 millivolts less V than transistor0, and this 60 millivolts thus appears across resistor 30. Since the AVbetween transistors Q, and Q has a positive temperature coefficient, thevoltage across resistor 30 increases with temperature at a rate which isdirectly proportional to absolute temperature and is quite linear. Thecollector current of transistor Q, is approximately equal to its emittercurrent if the B of the the transistor is high. Thus, the voltageproduced across resistor 24 is also directly proportional to temperatureand increases therewith.

For changes of current in transistor Q,. the collector current oftransistor Q, varies as the log of that change so as to produce anattenuation of current change between transistors Q, and Q For example,this means that if the current through transistor Q, changes by a factorof 2, the current through transistor Q will change by only a factor of0.3. Thus, to the first approximation, the current through transistor Qis relatively well stabilized against initial current variations intransistor 0,.

Transistor O is connected directly across the circuit points 20 and 28with its base coupled to the collector of 0,. Since the V of 0;,decreases as temperature increases, and a feedback loop is formed fromthe collector of Q, back'through resistor 30 and down to its base, aconstant current applied at point 20 by means of the source 34, causesthe base-to-emitter voltage of transistor Q, to change only withtemperature because its collector current is constant. The collectorvoltage of transistor 0;, is equal to its base-to-emitter voltage plusthe I voltage drop across resistor 24 caused by the collector current oftransistor (2,. By appropriately selecting the value of resister 24 anet zero temperature coefficient can be obtained for the voltage acrosspoints 20 and 28. In other words, the negative coefficient voltageacross the base-to-emitter of transistor 0 and the positive coefficientvoltage due to the current from transistor 6 a ci ossresistance 24 thusbalance each other to provide a net zero temperature coefficient. Thisrelationship is explained by the equations above. The reference voltageV, for the illustrated preferred embodiment is 1.205 volts.

Equation (7) sets the voltage relationships for zero temperaturecoefficients. However, the relationship remains if both sides aremultiplied by a constant. Understandably, a zero temperature coefficientreference can also be made at twice V by using two series transistorsfor V and a proportionately larger amount of AV The output voltage ofthe reference is not limited to integer values of V By using fractionalparts of V with a proportional part of AV any output voltage isobtainable.

The operational amplifier 12 is connected as a voltage follower havingthe characteristics that the input voltage and output voltage areexactly the same. Since the emitter of transistor O is connected to theinput terminal 36 of op-amp 12, and the collector thereof is connectedto the input terminal 38 through the resistor R, the collector oftransistor Q is going to be 1.205 volts above the output of the op-amp12 no matter what the output is since the output terminal 2 is coupleddirectly to the input 36 by the line 40. The amplifier 12 is a high-gainamplifier and has a high accuracy in terms of keeping its input andoutput voltages the same.

In the voltage follower configuration, the voltage between the plus andminus input must always be nearly zero. Therefore, by connecting theresistor R between the circuit point 20 and input terminal 3, there mustnecessarily be a constant voltage impressed across the resistor R. Thus,the current flowing from the voltage reference 14 into the terminal 3must necessarily be equal to 1.205 volts divided by the resistance r;and, since the plus input of the voltage follower 12 draws a negligibleamount of current, it can be said that all of the current flowingthrough resistor R also flows through the variable resistance 15 toground. The variable resistance 15 thereby serves as an adjustmentresistor for controlling the voltage appearing at the output terminal 2.

For example, with a constant 100' microamps flowing through resistor R,there will necessarily be 100 microamps flowing through the adjustmentresistor 15 to ground. The voltage at the plus input 38 of the voltagefollower 12 will thus be a function of the resistance of resistor 15 andthe 100 microamps current. And since the IOU-microamps current isconstant, the voltage at the plus input will be directly related to theresistance of resistor 15. Moreover, since the voltage at outputterminal 2 is directly related to the input voltage applied at terminal3, it will be seen that the voltage applied across the entire regulatoris equal to V,,,V and is in no way referenced to ground. It is thus afloating voltage regulator and is capable of regulating any voltage solong as V -V is less than the breakdown potential of the circuitelements.

As will be understood from the above, the basis for operation of theregulator is that a constant current is provided which is directedthrough an adjustment resistor in order to obtain the desired regulatedvoltage and the only requirement insofar as what voltage may beregulated at output terminal 2, is that the difference between theoutput voltage and the unregulated input voltage must not exceed thevoltage handling capabilities of the regulator circuit 10.

Turning now to Figure 3 of the drawing, a simplified schematic diagramof a preferred embodiment of the invention is illustrated. lt will benoted, however, that in the voltage reference circuit 11 an additionaltransistor Q. has been connected across circuit points and 28 and aresistor 27 has been added to the collector circuit of transistor QSince the reference voltage at circuit point 20 is proportional to thebaSeto-emitter voltage of transistor 0;, plus the voltage acrossresistor 27, the base-to-emitter voltage of transistor Q should be 5, asas possible. One way of doing this m mnmm, m which absorbs currentchanges from the current source 34, and since its base current changes asmall friction of the amount of any current change (i.e., the basecurrent change oftranfioTQi is equal to the change in current to 0.,divided by the transistor sees a very small change in collector current.Transistor 0 increases the gain of the reference against changes incurrent flow. Although it is not necessary to the invention, one wouldnormally add such a transistor in practice in order to make thereference more stable with respect to input voltage changes. As in theFigure 2 embodiment, the resistor R sets the value of the currentflowing into the adjustment terminal 3.

The voltage follower 12 is made up of three stages, namely a firstdifferential amplifier 50, a second differential amplifier 52 and anemitter follower 54. The amplifier 50 is comprised of the transistors QQ Q and 0,; along with the resistors 56 and 58. The base of transistorQ, forms the positive input to op-amp 12 and is coupled to theadjustment terminal 3. The base of transistor Q forms a negative inputto op-amp 12 and is coupled to the lead 29 which is common with theoutput terminal 2 and circuit point 28. Current sources 60 and 62 areprovided as indicated for energizing the amplifier. A voltage differenceacross the collectors of transistor Q and Q9 (i.e.,

across resistors 56 and 58) is proportional to the difference in voltagebetween the base of transistor 0 and the base of transistor 0 Thecircuit is balanced if the inputs to transistor 0,, and Q, are the sameand no difference voltage is generated between the collector oftransistors q, and q,,. Because of the resistors 56 and 58, theamplifier 50 forms a differential gain stage the output of which iscoupled into the differential amplifier 52.

The base of transistor 0 is coupled to the collector of transistor Q andthe base of transistor Q10 is coupled to the collector of transistor Qso that the second differential amplifier 52 is also balanced when thecollector voltages of transistors 0 and Q; are the same. In other words,the amplifier 52 responds to voltage differentials across the collectorsof transistors Q and 0 A current source 64 couples the collector oftransistor Q to the input terminal and a resistor 66 couples the emitterof transistors Q and On; to the common line 29.

The output of amplifier 52 is taken at the collector of transistor Q1and feeds the emitter follower circuit 54 which is comprised of thetransistors Q and O and which provides current gain in the output forthe circuit. Since the emitter of Q is tied to the common line 29, itwill be noted that the output thereof is coupled back to the base oftransistor 0 to provide negative feedback for the circuit.

The operation of the circuit can be explained as follows: Suppose thevoltage at the base of transistor 0,, is caused to go positive as wouldbe the case if one were to increase the resistance of resistor 15. Thiswould reduce the base-to-emitter voltage of transistor 0 causing it toturn off. The turning off of transistor Q accordingly reduces thebase-to-emitter voltage of transistor Q causing it to turn off. Whenthis happens, the differential amplifier Q turns on. Since Q, is turningoff, its voltage will rise and the voltage at the collector oftransistor Q will decrease since it is turning on. The resultant currentflow through resistors 56 and 58 will then provide a differentialvoltage at the bases of transistors Q and Q") which tends to turntransistor Q off causing more current from the current source 64 to goto the base of transistor Q turning the emitter follower 54 harder on soas to bring the potential of V at terminal 2 up.

Since terminal 2 is connected through common lead 29 to the base oftransistor Q.;, a servo loop is completed which terminates the increasein potential at terminal 2 when the base of transistor 0 reaches thesame potential as the base of transistor Q This is to say that theoutput of emitter follower 54 acts to turn off the source which drivesit so as to effectively keep the potential at the output terminal 2exactly equal to the potential at terminal 3. Although the differentialstage 52 is added to increase the gain and provide greater accuracy inthe voltage follower 54, as well as providing greater isolation betweenthe adjustment and the output, it could actually be eliminated, in whichcase the base of transistor Q11 would be 005E610 the cbllector oftransistor 6,. The preferred embodiment however, uses both stages forthe reasons described above.

This circuit can regulate any voltages from volts upwards since theregulator is completely floating and sees only the difference inpotential across terminals 1 and 2. As mentioned above, the onlyrequirement is that the difference between the voltage applied to theinput terminal 1 and the output voltage at output terminal 2 be keptless than the breakdown potential of the transistors in the circuit.Appropriate modifications of the transistors Q and Q can be made toaccommodate the various load requirements which might be encountered. Inother words, the circuit as described will regulate very high voltagesas well as very low voltages. For instance, a 300-volt output atterminal 2 could be regulated with the circuit described. However, sincethe breakdown potential of the integrated circuit transistors in thecircuit is about 50 volts, this would mean that the maximum inputvoltage would have to be less than 350 volts in order to prevent damageto the circuit.

Turning now to Figure 4 of the drawing, a current regulator is shownwhich utilizes the same three-terminal circuit as is shown in thevoltage regulator embodiments above, except that the bottom side of theadjustment resistor 15 is no longer connected to ground but is insteadconnected to an external output terminal 4 which is connected to theoutput terminal 2 by a resistor 70. A current flowing through resistor15 to terminal 4 and generating a l-volt drop thereacross causes thepositive input 38 of the amplifier 12 to see a voltage which is due tothe resistance 15. However, since the potentials at the input and outputof amplifier 12 must be identical, there must be a one volt rise acrossresistor 70 from terminal 4 to terminal 2 so as to cancel any differencein potential between terminals 2 and 3. Therefore, the current flowingthrough resistor 70 and available at the output terminal 4 will beindependent of the load receiving the current flow but will be directlyproportional to the resistive value of resistor 15.

Whereas, previous regulators have required that zener diodes be used inthe voltage reference, the present invention requires no zener diodeswhatsoever and all active components may be comprised of simpleintegrated circuit transistors. In addition, the fact that the presentinvention utilizes transistors which are well behaved and understood,means that the invention can be designed to be quite stable andsubstantially less noisy than a zener diode circuit in terms of smallvariations in voltage. For example, a circuit of this type will have anoise level of less than microvolts whereas most zener diode circuitshave noise levels which exceed a millivolt. The regulator as shown isfor positive voltages. For negative voltages, complementary transistorscan be used in a similar circuit.

After having read the above disclosure, it is contemplated that manyalterations and modifications of the invention will be apparent to thoseskilled in the art. It is therefore to be understood that this is adescription of a preferred embodiment and is made solely for purposes ofillustration rather than limitation. Accordingly, it is intended thatthe appended claims be interpreted as covering all modifications whichfall within the true spirit and scope of the invention.

What is claimed is:

1. An electrical regulator circuit, comprising:

an input terminal for receiving an unregulated input voltage;

an output terminal;

an adjustment terminal;

means for developing a reference voltage having a substantially zerotemperature coefficient and including,

a first terminal coupled to said input terminal,

a second terminal,

a third terminal,

a first transistor having a first emitter coupled to said secondterminal, a first collector coupled to said third terminal, and a firstbase coupled to said first collector,

a second transistor having a second base coupled to said firstcollector, a second collector coupled to said third terminal, and asecond emitter coupled to said second terminal, said first and secondtransistors having different current densities J and J respectively,whereby the base-to-emitter differential AV therebetween has a positivetemperature coefficient and may be expressed as where k is Boltzmannsconstant, T is absolute temperature, and q is the charge on an electron,and

circuit means having a negative temperature coefficient operativelycombined with said first and second transistors to develop saidreference voltage between said second and third terminals,

a resistive impedance coupling said third terminal to said adjustmentterminal; and

voltage follower means operatively coupling said input terminal to saidoutput terminal and having a first input terminal coupled to said secondterminal and a second input terminal coupled to said adjustmentterminal, said voltage follower means being responsive to a voltagedeveloped at said adjustment terminal when said adjustment terminal isresistively coupled to a circuit ground and said unregulated inputvoltage is applied between said input terminal and said circuit ground,said voltage follower means being operative to develop a regulatedvoltage at said output terminal.

2. An electrical regulator circuit as recited in claim 1 wherein saidcircuit means includes a third transistor having a third base coupled tosaid second collector, a third emitter coupled to said second terminaland a third collector coupled to said third terminal, said negativetemperature coefficient being a function of the base-to-emitter voltageV of said third transistor.

3. An electrical regulator circuit as recited in claim 2 wherein saidreference voltage may be expressed as where a, b and c are constants.

4. An electrical regulator circuit as recited in claim 2 and furthercomprising a fourth transistor having a fourth base coupled to saidthird collector, a fourth emitter coupled to said third terminal. and afourth collector coupled to said second terminal.

5. An electrical regulator circuit as recited in claim 1 wherein saidvoltage follower means includes, a first differential amplifierresponsive to the voltage developed between said second terminal andsaidadjustment terminal and operative to develop a control signal, andan emitter follower amplifier responsive to said control signal andoperative to control current flow between said input terminal and saidoutput terminal thereby developing a regulated voltage at said outputterminal.

6. An electrical regulator circuit as recited in claim 5 and furthercomprising a second differential amplifier operatively coupling saidfirst differential amplifier to said emitter follower amplifier 7. Anelectrical regulator circuit as recited in claim 1 and furthercomprising an external terminal, a variable resistive impedance couplingsaid adjustment terminal to said external terminal, and an externalresistive impedance coupling said external terminal to said outputterminal whereby a regulated current is provided at said externalterminal.

8. An electrical regulator circuit as recited in claim 1 and furthercomprising a variable resistive impedance for coupling said adjustmentterminal to the circuit ground, the regulated voltage being selectableby varying said variable resistive impedance.

9. A voltage reference circuit, comprising:

a first terminal and a second terminal;

first circuit means for developing a first voltage which increases withtemperature and including,

a first transistor having a first emitter coupled to said secondterminal, a first collector coupled to said first terminal, and a firstbase coupled to said first collector, and

a second transistor having a second base coupled to said firstcollector, a second emitter coupled to said second terminal, and asecond collector coupled to said first terminal; and

second circuit means for developing a second voltage which decreaseswith temperature and including, a third transistor having a third basecoupled to said second collector, a third emitter coupled to said secondterminal and a third collector coupled to said first terminal, saidfirst and second voltages being combined to develop a reference voltageacross said first and second terminals.

10. A voltage reference circuit as recited in claim 9 wherein saidreference voltage may be expressed as reI b Ba' aa where a, b and c areconstants,

V is the base-to-emitter voltage of said third transistor,

and

AV is the base-to-emitter differential between said first and secondtransistors.

11. A voltage reference as recited in claim 9 and further comprising afourth transistor having a fourth base coupled to said third collector,a fourth emitter coupled to said first terminal, and a fourth collectorcoupled to said second terminal.

12. An electrical regulator circuit, comprising:

an input terminal for receiving an unregulated input voltage;

an output terminal;

an adjustment terminal; means for developing a reference voltage havinga substantially zero temperature coefficient and including,

a first terminal coupled to said input terminal,

a second terminal,

a third terminal,

a first transistor having a first emitter coupled to said secondterminal, a first collector coupled to said third terminal, and a firstbase coupled to said first collector,

a second transistor having a second base coupled to said firstcollector, a second collector coupled to said third terminal, and asecond emitter coupled to said second terminal, and

circuit means having a negative temperature coefficient operativelycombined with said first and second transistors to develop saidreference voltage between said second and third terminals,

a resistive impedance coupling said third terminal to said adjustmentterminal; and

voltage follower means operatively coupling said input terminal to saidoutput terminal and having a first input terminal coupled to said secondterminal and a second input terminal coupled to said adjustmentterminal, said voltage follower means being responsive to a voltagedeveloped at said adjustment terminal when said adjustment terminal isresistively coupled to a circuit ground and said unregulated inputvoltage is applied between said input terminal and said circuit ground,said voltage follower means being operative to develop a regulatedvoltage at said output terminal.

II! I t i

1. An electrical regulator circuit, comprising: an input terminal forreceiving an unregulated input voltage; an output terminal; anadjustment terminal; means for developing a reference voltagE having asubstantially zero temperature coefficient and including, a firstterminal coupled to said input terminal, a second terminal, a thirdterminal, a first transistor having a first emitter coupled to saidsecond terminal, a first collector coupled to said third terminal, and afirst base coupled to said first collector, a second transistor having asecond base coupled to said first collector, a second collector coupledto said third terminal, and a second emitter coupled to said secondterminal, said first and second transistors having different currentdensities J1 and J2 respectively, whereby the base-to-emitterdifferential Delta VBE therebetween has a positive temperaturecoefficient and may be expressed as Delta VBE (kT/q)1n(J1J2) where k isBoltzmann''s constant, T is absolute temperature, and q is the charge onan electron, and circuit means having a negative temperature coefficientoperatively combined with said first and second transistors to developsaid reference voltage between said second and third terminals, aresistive impedance coupling said third terminal to said adjustmentterminal; and voltage follower means operatively coupling said inputterminal to said output terminal and having a first input terminalcoupled to said second terminal and a second input terminal coupled tosaid adjustment terminal, said voltage follower means being responsiveto a voltage developed at said adjustment terminal when said adjustmentterminal is resistively coupled to a circuit ground and said unregulatedinput voltage is applied between said input terminal and said circuitground, said voltage follower means being operative to develop aregulated voltage at said output terminal.
 2. An electrical regulatorcircuit as recited in claim 1 wherein said circuit means includes athird transistor having a third base coupled to said second collector, athird emitter coupled to said second terminal and a third collectorcoupled to said third terminal, said negative temperature coefficientbeing a function of the base-to-emitter voltage VBE of said thirdtransistor.
 3. An electrical regulator circuit as recited in claim 2wherein said reference voltage may be expressed as Vref a(bVBE+c DeltaVBE) where a, b and c are constants.
 4. An electrical regulator circuitas recited in claim 2 and further comprising a fourth transistor havinga fourth base coupled to said third collector, a fourth emitter coupledto said third terminal, and a fourth collector coupled to said secondterminal.
 5. An electrical regulator circuit as recited in claim 1wherein said voltage follower means includes, a first differentialamplifier responsive to the voltage developed between said secondterminal and said adjustment terminal and operative to develop a controlsignal, and an emitter follower amplifier responsive to said controlsignal and operative to control current flow between said input terminaland said output terminal thereby developing a regulated voltage at saidoutput terminal.
 6. An electrical regulator circuit as recited in claim5 and further comprising a second differential amplifier operativelycoupling said first differential amplifier to said emitter followeramplifier
 7. An electrical regulator circuit as recited in claim 1 andfurther comprising an external terminal, a variable resistive impedancecoupling said adjustment terminal to said external terminal, and anexternal resistive impedance coupling said external terminal to saidoutput terminal whereby a regulated current is provided at said externalterminal.
 8. An electrical regulator circuit as recited in claim 1 andfurther comprising a variable resistive impedance for coupling saidadjustment terminal to the circuit ground, the reGulated voltage beingselectable by varying said variable resistive impedance.
 9. A voltagereference circuit, comprising: a first terminal and a second terminal;first circuit means for developing a first voltage which increases withtemperature and including, a first transistor having a first emittercoupled to said second terminal, a first collector coupled to said firstterminal, and a first base coupled to said first collector, and a secondtransistor having a second base coupled to said first collector, asecond emitter coupled to said second terminal, and a second collectorcoupled to said first terminal; and second circuit means for developinga second voltage which decreases with temperature and including, a thirdtransistor having a third base coupled to said second collector, a thirdemitter coupled to said second terminal and a third collector coupled tosaid first terminal, said first and second voltages being combined todevelop a reference voltage across said first and second terminals. 10.A voltage reference circuit as recited in claim 9 wherein said referencevoltage may be expressed as Vref a(bVBE+c Delta VBE) where a, b and care constants, VBE is the base-to-emitter voltage of said thirdtransistor, and Delta VBE is the base-to-emitter differential betweensaid first and second transistors.
 11. A voltage reference as recited inclaim 9 and further comprising a fourth transistor having a fourth basecoupled to said third collector, a fourth emitter coupled to said firstterminal, and a fourth collector coupled to said second terminal.
 12. Anelectrical regulator circuit, comprising: an input terminal forreceiving an unregulated input voltage; an output terminal; anadjustment terminal; means for developing a reference voltage having asubstantially zero temperature coefficient and including, a firstterminal coupled to said input terminal, a second terminal, a thirdterminal, a first transistor having a first emitter coupled to saidsecond terminal, a first collector coupled to said third terminal, and afirst base coupled to said first collector, a second transistor having asecond base coupled to said first collector, a second collector coupledto said third terminal, and a second emitter coupled to said secondterminal, and circuit means having a negative temperature coefficientoperatively combined with said first and second transistors to developsaid reference voltage between said second and third terminals, aresistive impedance coupling said third terminal to said adjustmentterminal; and voltage follower means operatively coupling said inputterminal to said output terminal and having a first input terminalcoupled to said second terminal and a second input terminal coupled tosaid adjustment terminal, said voltage follower means being responsiveto a voltage developed at said adjustment terminal when said adjustmentterminal is resistively coupled to a circuit ground and said unregulatedinput voltage is applied between said input terminal and said circuitground, said voltage follower means being operative to develop aregulated voltage at said output terminal.